Does anyone know a good subwoofer for a 3 cu-ft sealed box? I will use it for movies and music concerts. I have a KG5230 amplifier and this speaker will be a replacement for a old NHT1259 that is broken.

I'm not sure just what your design goals are (cost, size, freq resp...etc), so I'll just mention the two subs that I'd buy tomorrow if I was building another sub. I think my first choice would be the "Alpine R series" driver. If I didn't already have two JL Audio subs in my box for a four 10 project that I just finished, I would definitely have used these.

I like them because they come so highly recommended first off. They will take a ton of punishment, they're focused on "sound quality", they've also got 20mm of linear X-max and don't mind being forced downward into low 20's. The link that I'll give you is for the ten inch, but they'll all perform the exact same way, so just look at the size that you're interested in. I like the "Dual" 4 ohm voice coil for it's flexibility, but again, I don't know what your application requirements are. Here's that link: Alpine SWR-10D4 (swr10d4) 10" Dual 4-Ohm Type-R Series Car Subwoofer

Then, there's the one that I use myself. It's the JL Audio "10W6-v2", again, you choose the size. I like these for the same reasons that I like the Alpine R series; It's the proven workhorse. Here's that link: Car Audio - Subwoofer Drivers - Discontinued - W6v2 (discontinued to make room for version 3 "W6-v3", but still available). Btw, you said that the enclosure that your planning to use is 3 cu ft net? That's quite a lot; enough intern volume to "Double up" on these subs. Both of these drivers require only (approx) .625 net int vol., so you could increase the efficiency, low-end extension...and, lower system impedance simply by using two subs in that box instead of one; that's about 6db of "Free output"!

Now these are both primarily used in mobile audio applications, but they are also recommend for HT, and warrantied for one yr. Hope you find this little bit of info helpful, I only wish I had more insight as to what your project objectives are so I could better assist.

Thank you for the recommendations. My goal is a 12" sub that will be driven by a 300w amp. I plan to cutoff at 100-150hz. My room is 750 sq-ft without openings. It is big but I don't play that loud.

Cost does not matter right now because I want to see all the options I have. I need a "drop-fit" speaker to use this 3 cu-ft sealed box and the 300w KG5230 amp.

If the speaker requires a smaller box, I can put wood blocks inside of it to lower the volume.

Hi Guijs,

Both the drivers that I've suggested are extremely forgiving, and won't mind being in the larger enclosure. The (2) ten sub that I'm using now was once intended to be used as a "bass reflex" alignment, with a total net vol of 2.50 cu ft (1.25 cf per driver; box is "partitioned"), but I "sealed" it, bringing the net volume up to 3.2 cf (1.6 cf per driver).

PS: when you calculate the internal vol of a vented enclosure, you have to subtract the total displacement of the ports (in cf) from your gross figure. But, when you "close-up" those ports, you no longer see them as parts, occupying space so you add that space to your net vol.

rigtec, but you mean that I should use (1) or (2) 12" speakers? I can't cut a second hole to fit two speakers.

I know JL from my car stereo days, they are very good!

You can use just one 12. To determine just how the driver will behave in a box that size though, I would model (simulate) it using a speaker software design program like, winISD or bassbox pro...etc, which can be downloaded (for free) to your computer. I did it with the the "10W6", putting it in a 5 cf box, and the results were most favorable. You're not using much power anyway, so there'd be no "over excursion" issues to be concerned with; just x-over point fine tuning.

The only further concern (for me), might be, the "lack of available power" from the amp. Remember, most subs average around 82-84db of sensitivity @1w/1m (meaning,1 watt fed into an 8 ohm speaker, then measuring it's audible output with a decibel meter, located at only 1 meter away from the cone's center). So if 1 watt fed to the sub gives you 84db, then 300 watts (256 to be accurate) will give you 108db max; "that's not very loud". But, don't plan on using the whole 300 watts from the amp because it won't sound very good at that level (you know...the whole thing about "total harmonic distortion" and "square waves", screwing up the sound and causing the sub's motor to lose control over the cone...blah, blah, blah).

I have always used this as a rule of thumb, "and it works": "No less" than 1.5 decibels of "Headroom" for bass, or "at least"...3db for sub-bass. Three db is equivalent to 100% of the power planned to use; or double, that same amount of power. So for you, 600 watts "might be", a good place to start (only a suggestion). Anyway, it's more healthy for the amp to have enough power to destroy the driver, yet enough control over it's coil, to prevent the amp from doing so; That's Electro-Voice..."The proper care and feeding of pro-sound woofers"...a great read.

Let me know how you're making out Guijs, like to see some pics of your project as it's in development!